Recent cross-sectional studies in man have identified two important alterations in the secretion of AVP with advancing age. These are (1) augmented AVP secretion in response to osmotic stimulation and (2) escape from the inhibitory influence of intravenous ethanol on AVP secretion. The studies outlined in this proposal will determine the influence of age, volume status and plasma AVP concentration on the volume of distrbution and metabolic clearance rate of exogenous vasopressin. Several aspects of the influence of age on AVP secretion will be studied. These include clarification of the influence of volume expansion and depletion on the previously documented increased osmoreceptor sensitivity with age, the impact of aging on response to hypoosmolar inhibition of AVP release, and the impact of age on the response to several non-osmolar stimuli of AVP secretion. Non-osmolar stimuli to be employed are (1) upright posture and (2) pharmacologic stimuli (apomorphine, luteinizing hormone releasing factor (LHRH) and thyrotropic releasing factor (TRH).